A transmitting apparatus as one of electronic devices is also often installed outside a station building and, in such a case, the transmitting apparatus needs to operate at an environmental temperature ranging from −40° to +65°.
In such a temperature environment, a transmitting apparatus is mounted with a forced-air-cooling fan (FAN) therein for ventilation as a measure especially against a high temperature and the role of the fan is important to improve the reliability of the apparatus.
Controlling the number of revolutions of the forced-air-cooling fan in response to the variation of the temperature can be considered. However, to achieve this, a configuration that is adapted to detect the environmental temperature and feedback it to a circuit that controls the number of revolutions is necessary.
However, such a feedback configuration is difficult to employ in terms of the cost of the apparatus, etc.
On the other hand, as a technique concerning the control of revolution of a fan, a technique is known, for controlling the revolution of a cooling fan for a housing of a plurality of packages that are mounted in an information processing apparatus (see Patent Document 1: Japanese laid open patent publication Tokukai-Hei 8-30357).
The technique described in Patent Document 1 determines, in response to the number of the packages mounted in the apparatus, the number of cooling fans for which the revolution is controlled by the technique, or the number of revolutions of each of the fans.
That is, in the above conventional example, the number of cooling fans or the number of revolutions of each of the fans are determined in response to the power consumption determined by the number of the packages mounted in the apparatus.
On the other hand, as practical operation, conventionally, filters (Filter) have been equipped corresponding to fans and a constant amount of air flow has been maintained by replacing the filters at a proper interval by a user to avoid clogging of the filters. In such a case, a work of replacing the filters at a proper interval considering the clogging is necessary for the user.
In such a case, because the number of revolutions of the fans is constant immediately after the replacement of the filters compared to that before the replacement, the amount of air flow sent to the apparatus has become significantly different and it is difficult to maintain the temperature in the apparatus within a pre-determined range.
Because a minimum amount of air flow needs to be continuously sent regardless of the clogging of the filters, the number of revolutions often results in a number that is more than needed, and this leads to waste of the power consumption of the fans themselves.
For example, a sufficient amount of air flow can be supplied with 1000 revolutions immediately after the replacement of a filter. However, assuming that approximately 10,000 revolutions is necessary when the clogging is heavy, in a conventional apparatus, a fan needs to be continuously operated at 10,000 revolutions including the technique described in Patent Document 1, and extra power is necessary.